U.S. patent application number 10/998624 was filed with the patent office on 2006-06-08 for variable discharge fuel pump.
This patent application is currently assigned to Caterpillar Inc.. Invention is credited to Brad E. Bartley, Gregory W. Hefler, Kevin Charles Reynolds, Scott F. Shafer.
Application Number | 20060120880 10/998624 |
Document ID | / |
Family ID | 35601396 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060120880 |
Kind Code |
A1 |
Shafer; Scott F. ; et
al. |
June 8, 2006 |
Variable discharge fuel pump
Abstract
A pump has a housing defining a first pumping chamber and a
second pumping chamber. The pump also has a first plunger and a
second plunger. The pump additionally has at least one driver
operatively engaged with at least one of the first and second
plungers to move the at least one of the first and second plungers
between first and second end positions. The pump further has a
common spill passageway fluidly connectable to the first and second
pumping chambers and a selector valve disposed between the common
spill passageway and the first and second pumping chambers. The
selector valve has a body and a ball valve member operably disposed
within the body. The ball valve member is movable between a first
and a second ball valve member position to selectively fluidly
connect the first and second pumping chambers to the common spill
passageway.
Inventors: |
Shafer; Scott F.; (Morton,
IL) ; Bartley; Brad E.; (Manito, IL) ;
Reynolds; Kevin Charles; (Kent, GB) ; Hefler; Gregory
W.; (Chillicothe, IL) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
Caterpillar Inc.
|
Family ID: |
35601396 |
Appl. No.: |
10/998624 |
Filed: |
November 30, 2004 |
Current U.S.
Class: |
417/245 ;
417/244 |
Current CPC
Class: |
F04B 49/24 20130101;
F02M 59/366 20130101; F02M 59/365 20130101 |
Class at
Publication: |
417/245 ;
417/244 |
International
Class: |
F04B 3/00 20060101
F04B003/00; F04B 5/00 20060101 F04B005/00 |
Claims
1. A pump, comprising: a housing defining a first pumping chamber
and a second pumping chamber; a first plunger slidably disposed
within the first pumping chamber and movable between a first and a
second spaced apart end position to pressurize a fluid; a second
plunger slidably disposed within the second pumping chamber and
movable between the first and second spaced apart end positions to
pressurize the fluid; at least one driver operatively engaged with
at least one of the first and second plungers to move the at least
one of the first and second plungers between the first and second
end positions; a common spill passageway fluidly connectable to the
first and second pumping chambers; and a selector valve disposed
between the common spill passageway and the first and second
pumping chambers, the selector valve having: a body; and a ball
valve member operably disposed within the body, the ball valve
member being movable between a first and a second ball valve
position to selectively fluidly connect the first and second
pumping chambers to the common spill passageway.
2. The pump of claim 1, wherein the body includes a through fluid
passageway connecting the first and second pumping chambers, the
ball valve member being disposed within the through fluid
passageway.
3. The pump of claim 2, wherein the through fluid passageway is a
first fluid passageway and the body further includes a second fluid
passageway fluidly connecting the first fluid passageway with the
common spill passageway.
4. The pump of claim 1, wherein the selector valve further
includes: a first valve seat; and a second valve seat, the ball
valve member being disposed between the first and second valve
seats and configured to selectively engage the first and second
valve seats.
5. The pump of claim 4, wherein the first valve seat is integral to
the body and the second valve seat is separate from the body, the
second valve seat being connected to the body during assembly of
the pump.
6. The pump of claim 4, wherein the second valve seat is pressed
into the body during assembly of the pump.
7. The pump of claim 6, wherein the second valve seat has at least
one point of contact with the housing.
8. The pump of claim 1, wherein the body is pressed into the
housing during assembly of the pump.
9. The pump of claim 1, further including a high-pressure outlet in
fluid communication with the first and second pumping chambers.
10. The pump of claim 9, further including: a spill control valve
disposed within the common spill passageway, the spill control
valve having a first spill control valve position at which fluid
flows from one of the first and second pumping chambers through the
spill control valve and a second spill control valve position at
which the spill control valve blocks the flow of fluid; a first
outlet check valve disposed between the first pumping chamber and
the high-pressure outlet, the first outlet check valve having a
first outlet check valve position at which fluid flows from the
first pumping chamber through the first outlet check valve and a
second outlet check valve position at which the first outlet check
valve blocks the flow of fluid from the first pumping chamber; and
a second outlet check valve disposed between the second pumping
chamber and the high-pressure outlet, the second outlet check valve
having a first outlet check valve position at which fluid flows
through the second outlet check valve and a second outlet check
valve position at which the second outlet check valve blocks the
flow of fluid.
11. The pump of claim 1, wherein the first plunger in the first
pumping chamber reciprocates out of phase with the second plunger
in the second pumping chamber.
12. The pump of claim 1, further including: a first supply
passageway in selective fluid communication with the first pumping
chamber; and a second supply passageway in selective fluid
communication with the second pumping chamber.
13. The pump of claim 1, wherein the at least one driver is a first
driver and the pump further includes a second driver operatively
engaging the other of the first and second plungers to move the
other of the first and second plungers between the first end
position and the second end position.
14. A method of operating a pump, comprising: moving a first
plunger within a first pumping chamber from a second end position
to a first end position to draw a fluid into the first pumping
chamber; moving the first plunger from the first end position to
the second end position to pump the fluid through a common spill
passageway; moving a second plunger within a second pumping chamber
from a second end position to a first end position to draw a fluid
into the second pumping chamber; moving the second plunger from the
first end position to the second end position to pump the fluid
through the common spill passageway; and moving a ball valve member
within a selector valve body between a first ball valve position
and a second ball valve position to selectively fluidly communicate
the first and second pumping chambers with the common spill
passageway.
15. The method of claim 14, further including: blocking the common
spill passageway to build pressure within the first and second
pumping chambers; and passing the pressurized fluid through a
high-pressure outlet during movement between the first end
positions and the second end positions.
16. The method of claim 14, further including: moving a spill valve
member from a first spill valve position to a second spill valve
position to block the common spill passageway; holding the spill
valve member in the second spill valve position with fluid
pressure; moving a first outlet check valve from a second outlet
check valve position to a first outlet check valve position with
fluid pressure to pass the pressurized fluid from the first pumping
chamber; and moving a second outlet check valve from a second
outlet check valve position to a first outlet check valve position
with fluid pressure to pass the pressurized fluid from the second
pumping chamber.
17. A fuel system, comprising: a reservoir of fluid; a plurality of
fuel injectors; a fuel rail in fluid communication with the
plurality of fuel injectors; and a pump in fluid communication with
the reservoir and the fuel rail, the pump having: a housing
defining a first pumping chamber and a second pumping chamber; a
first plunger slidably disposed within the first pumping chamber
and movable between a first and a second spaced apart end position
to pressurize a fluid; a second plunger slidably disposed within
the second pumping chamber and movable between the first and second
spaced apart end positions to pressurize the fluid; at least one
cam operatively engaged with at least one of the first and second
plungers to move the at least one of the first and second plungers
between the first end position and the second end position; a
common spill passageway fluidly connectable to the first and second
pumping chambers; a selector valve disposed between the common
spill passageway and the first and second pumping chambers, the
selector valve having: a body; and a ball valve member operably
disposed within the body, the ball valve member being movable
between a first and a second ball valve position to selectively
fluidly connect the first and second pumping chambers to the common
spill passageway; and a high-pressure outlet in fluid communication
with the first and second pumping chambers, the high-pressure
outlet passing pressurized fluid into the fuel rail.
18. The fuel system of claim 17, wherein the body includes a
through fluid passageway connecting the first and second pumping
chambers, the ball valve member being disposed within the through
fluid passageway.
19. The fuel system of claim 18, wherein the through fluid
passageway is a first fluid passageway and the body further
includes a second fluid passageway fluidly connecting the first
fluid passageway with the common spill passageway.
20. The fuel system of claim 17, wherein the selector valve further
includes: a first valve seat; and a second valve seat, the ball
valve member being disposed between the first and second valve
seats.
21. The fuel system of claim 20, wherein the first valve seat is
integral to the body and the second valve seat is separate from the
body, the second valve seat being connected to the body during
assembly of the pump.
22. The fuel system of claim 21, wherein the second valve seat is
pressed into the body.
23. The fuel system of claim 22, wherein the second valve has at
least one point of contact with the housing.
24. The fuel system of claim 17, wherein the selector valve body is
pressed into the pump housing during assembly of the pump.
25. The fuel system of claim 17, further including: a spill control
valve disposed within the common spill passageway, the spill
control valve having a first spill control valve position at which
fluid flows from one of the first and second pumping chamber
through the spill control valve and a second spill control valve
position at which the spill control valve blocks the flow of fluid;
an first outlet check valve disposed between the first pumping
chamber and the high-pressure outlet, the first outlet check valve
having a first outlet check valve position at which fluid flows
from the first pumping chamber through the first outlet check valve
and a second outlet check valve position at which the first outlet
check valve blocks the flow of fluid from the first pumping
chamber; and a second outlet check valve disposed between the
second pumping chamber and the high-pressure outlet, the second
outlet check valve having a first outlet check valve position at
which fluid flows from the second pumping chamber through the first
outlet check valve and a second outlet check valve position at
which the second outlet check valve blocks the flow of fluid from
the second pumping chamber.
26. The fuel system of claim 17, wherein the first plunger in the
first pumping chamber reciprocates out of phase with the second
plunger in the second pumping chamber.
27. The fuel system of claim 17, further including: a first supply
passageway in selective fluid communication with the first pumping
chamber; and a second supply passageway in selective fluid
communication with the second pumping chamber.
28. The fuel system of claim 17, wherein the at least one cam is a
first cam and the fuel system further includes a second cam
operatively engaged with the other of the first and second plungers
to move the other of the first and second plungers between the
first end position and the second end position.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to a fuel pump, and
more particularly to a variable discharge fuel pump.
BACKGROUND
[0002] A variable discharge fuel pump is utilized to maintain a
pressurized fuel supply for a plurality of fuel injectors in a
common rail fuel system. For example, U.S. patent Publication No.
2004/0109768 (the '768 publication) to Sommars et al. teaches a
variable discharge high-pressure pump for use in a common rail fuel
injection system. In such common rail systems, the pump supplies
fuel to the common rail, which in turn supplies the fuel to the
injectors when the injectors are energized. The pump serves to
maintain the common rail at a desired pressure and does so by
associating a pressure driven disk-type shuttle valve with each
pump chamber. When one of the pump pistons is undergoing its
pumping stroke, the fuel displaced by the piston presses against
the shuttle valve to open a passageway allowing fuel to flow to the
common rail.
[0003] However, because the pump of the '768 publication uses a
disk-type shuttle valve, the pump may be expensive and difficult to
produce. In particular, the valve seating surfaces that mate with
the shuttle valve disk are formed through a time consuming
Electrical Discharge Machining (EDM) process, which utilizes
expensive manufacturing equipment. The amount of time required to
produce the disk-type shuttle valve seating surfaces, in
conjunction with expensive EDM manufacturing equipment, can
increase the cost of the pump. In addition, high temperatures
associated with EDM processes can adversely affect material
properties of the shuttle valve surfaces.
[0004] Further, because the disk-type shuttle valve relies on
surface sealing, tight process tolerances may be required to
produce the desired sealing characteristics. These tight process
tolerances can further increase the cost of the pump.
[0005] The disclosed fuel pump is directed to overcoming one or
more of the problems set forth above.
SUMMARY OF THE INVENTION
[0006] In one aspect, the present disclosure is directed to a pump
that includes a housing defining a first pumping chamber and a
second pumping chamber. The pump also includes a first plunger
slidably disposed within the first pumping chamber and movable
between first and second spaced apart end positions to pressurize a
fluid, and a second plunger slidably disposed within the second
pumping chamber and movable between first and second spaced apart
end positions to pressurize the fluid. The pump further includes at
least one driver operatively engaged with at least one of the first
and second plungers to move the at least one of the first and
second plungers between the first and second end positions. The
pump additionally includes a common spill passageway fluidly
connectable to the first and second pumping chambers and a selector
valve disposed between the common spill passageway and the first
and second pumping chambers. The selector valve has a body and a
ball valve member operably disposed within the body. The ball valve
member is movable between a first and second ball valve position to
selectively fluidly connect the first and second pumping chambers
to the common spill passageway.
[0007] In another aspect, the present disclosure is directed to a
method of operating a pump. The method includes moving a first
plunger within a first pumping chamber from a second end position
to a first end position to draw a fluid into the first pumping
chamber, and moving the first plunger from the first end position
to the second end position to pump the fluid through a common spill
passageway. The method further includes moving a second plunger
within a second pumping chamber from a second end position to a
first end position to draw a fluid into the second pumping chamber,
and moving the second plunger from the first end position to the
second end position to pump the fluid through the common spill
passageway. The method also includes moving a ball valve member
within a selector valve body between a first position and a second
position to selectively fluidly communicate the first and second
pumping chambers with the common spill passageway.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic illustration of a common rail fuel
system according to an exemplary embodiment of the present
disclosure;
[0009] FIG. 2 is an enlarged cross-sectional view of a fill and
spill portion of the pump of the system of FIG. 1; and
[0010] FIG. 3 is an enlarged cross-sectional view of a selector
valve portion of the fill and spill portion of FIG. 2.
DETAILED DESCRIPTION
[0011] Referring to FIG. 1, a fuel system 10 includes a fuel
transfer pump 12 that may transfer fuel from a low pressure
reservoir 14 to a high-pressure pump 16 via a fluid passageway 17.
High-pressure pump 16 may pressurize the fuel and direct the
pressurized fuel through fluid passageway 18 to a fuel rail 20 that
is in fluid communication with a plurality of fuel injectors 22 via
fluid passageways 24. Fuel injectors 22 may be fluidly connected to
reservoir 14 via a leak return passageway 26. An electronic control
module 28 may be in communication with an actuator 30 connected to
high-pressure pump 16 via a control communication line 32, and with
individual fuel injectors 22 via additional communication lines
(not shown).
[0012] High-pressure pump 16 may include a housing 34 defining a
first and second barrel 36, 38. High-pressure pump 16 may also
include a first plunger 40 slidably disposed within first barrel
36. First barrel 36 and first plunger 40 together may define a
first pumping chamber 42. High-pressure pump 16 may also include a
second plunger 44 slidably disposed within second barrel 38. Second
barrel 38 and second plunger 44 together may define a second
pumping chamber 46. It is contemplated that additional pumping
chambers may be included within high-pressure pump 16.
[0013] A first and second driver 48, 50 may be operably connected
to first and second plungers 40, 44, respectively. First and second
drivers 48, 50 may include any means for driving first and second
plungers 40, 44 such as, for example, a cam, a solenoid actuator, a
piezo actuator, a hydraulic actuator, a motor, or any other driving
means known in the art. A rotation of first driver 48 may result in
a corresponding reciprocation of first plunger 40, and a rotation
of second driver 50 may result in a corresponding reciprocation of
second plunger 44. First and second drivers 48, 50 may be
positioned relative to each other such that first and second
plungers 40, 44 are caused to reciprocate out of phase with one
another. First and second drivers 48, 50 may each include three
lobes such that one rotation of a pump shaft (not shown) connected
to first and second drivers 48, 50 may result in six pumping
strokes. Alternately, first and second drivers 48, 50 may include a
different number of lobes rotated at a rate such that pumping
activity is synchronized to fuel injection activity. It is
contemplated that a single driver may be configured to drive both
first and second plungers 40, 44.
[0014] High-pressure pump 16 may include an inlet 52 fluidly
connecting high-pressure pump 16 to fluid passageway 17.
High-pressure pump 16 may also include a low-pressure gallery 60 in
fluid communication with inlet 52 and in selective communication
with first and second pumping chambers 42, 46. A first inlet check
valve 58 may be disposed between low-pressure gallery 60 and first
pumping chamber 42 and may be configured to allow a flow of
low-pressure fluid from low-pressure gallery 60 to first pumping
chamber 42. A second inlet check valve 62 may be disposed between
low-pressure gallery 60 and second pumping chamber 46 and may be
configured to allow a flow of low-pressure fluid from low-pressure
gallery 60 to second pumping chamber 46.
[0015] High-pressure pump 16 may also include an outlet 54, fluidly
connecting high-pressure pump 16 to fluid passageway 18.
High-pressure pump 16 may include a high-pressure gallery 68 in
selective fluid communication with first and second pumping
chambers 42, 46 and outlet 54. A first outlet check valve 70 may be
disposed between first pumping chamber 42 and high-pressure gallery
68 and may be configured to allow a flow of fluid from first
pumping chamber 42 to high-pressure gallery 68. A second outlet
check valve 74 may be disposed between second pumping chamber 46
and high pressure gallery 68 and may be configured to allow a flow
of fluid from second pumping chamber 46 to high-pressure gallery
68.
[0016] High-pressure pump 16 may also include a first spill
passageway 64 selectively fluidly connecting first pumping chamber
42 and a second spill passageway 72. A spill control valve 66 may
be disposed within a common spill passageway 73 between first and
second spill passageways 64, 72 and low-pressure gallery 60 and may
be configured to selectively allow a flow of fluid from first and
second spill passageways 64, 72 to low-pressure gallery 60.
[0017] As illustrated in FIG. 2, the fluid connection between
pumping chambers 42, 46 and low pressure gallery 60 may be
established by a selector valve 76 having a valve body 75, a ball
valve member 77, a first valve seat 78, and a second valve seat 80,
which is oriented in opposition to first valve seat 78.
[0018] Second valve seat 80 may be integral to valve body 75 and
disposed within a through fluid passageway 81 of valve body 75,
while first valve seat 78 may be pressed into through fluid
passageway 81 during assembly. As illustrated in FIG. 3, the length
of first valve seat 78 is selected to make two point contacts 79
with housing 74 so that first valve seat 78 is constrained from
moving out of selector valve 76 under the influence of pumping
pressure forces. Referring to FIG. 2, ball valve member 77 may be
disposed within fluid passageway 81 and free to oscillate between
first and second valve seats 78, 80 to selectively allow fluid to
flow from one of first and second pumping chambers 42, 46 to common
spill passageway 73 via a fluid passageway 83. The spacing between
valve seats 78 and 80 may be such that ball valve member 77 never
blocks all fluid from fluid passageway 83. It is contemplated that
both first and second valve seats 78, 80 may alternately be
separate from valve body 75 and connected to valve body 75 during
assembly. It is further contemplated that the separate valve seats
may be connected to valve body 75 by means other than pressing such
as, for example, by threaded fastening, by welding, by chemical
bonding, or by any other means known in the art. After assembly of
ball valve member 77 and first valve seat 78, valve body 75 may be
pressed into a bore 85 within housing 34. It is contemplated that
valve body 75 may be connected to housing 34 by means other than
pressing such as, for example, threaded fastening, welding,
chemical bonding, or any other means known in the art.
[0019] Only one of first and second pumping chambers 42, 46 may be
fluidly connected to low pressure gallery 60 at a time. Because
first and second plungers 40, 44 may move out of phase relative to
one another, one pumping chamber may be at high-pressure (pumping
stroke) when the other pumping chamber is at low-pressure (intake
stroke), and vice versa. This action may be exploited to move ball
valve member 77 back and forth to fluidly connect either first
spill passageway 64 to spill control valve 66, or second spill
passageway 72 to spill control valve 66. Thus, first and second
pumping chambers 42, 46 may share a common spill control valve
66.
[0020] For example, when first plunger 40 moves through a pumping
stroke and second plunger 44 moves through an intake stroke, ball
valve member 77 may be in the position illustrated in FIG. 2, in
which first pumping chamber 42 is fluidly connected to spill
control valve 66. The fluid connection between first pumping
chamber 42 and spill control valve 66 is created when fluid,
pressurized by first pumping chamber 42 acting on ball valve member
77, pushes ball valve member 77 to engage valve seat 80 and close
second spill passageway 72 from spill control valve 66. In similar
fashion, as second plunger 44 moves through the pumping stroke and
first plunger 40 moves through the intake stroke, ball valve member
77 may move to engage valve seat 78, thereby connecting second
spill passageway 72 to spill control valve 66, while low-pressure
fuel is drawn into first pumping chamber 42 past first inlet check
valve 58.
[0021] Spill control valve 66 may include a spill valve member 82
having a hydraulic surface 84 that produces a latching affect when
spill valve member 82 is in contact with a valve seat 86. Spill
valve member 82 may be normally biased toward a first position
where fluid is allowed to flow past spill valve member 82, as shown
in FIG. 2, via a biasing spring 88. Spill valve member 82 may also
be moved to a second position where fluid is blocked from flowing
past spill valve member 82 by energizing actuator 30. Actuator 30
may include a solenoid 31 configured to attract an armature 90
coupled to spill valve member 82 when solenoid 31 is energized,
thereby closing spill valve member 82. One skilled in the art will
recognize that actuator 30 may be any type of actuator known in the
art such as for example, a piezo and/or piezo bender actuator.
[0022] Control signals generated by electronic control module 28
directed to high-pressure pump 16 via communication line 32 may
determine when and how much fuel is pumped into fuel rail 20.
Control signals generated by electronic control module 28 directed
to fuel injectors 22 may determine the actuation timing and
actuation duration of fuel injectors 22.
[0023] Electronic control module 28 may include all the components
required to perform the required system control such as, for
example, a memory, a secondary storage device, and a processor,
such as a central processing unit. One skilled in the art will
appreciate that electronic control module 28 can contain additional
or different components. Associated with electronic control module
28 may be various other known circuits such as, for example, power
supply circuitry, signal conditioning circuitry, and solenoid
driver circuitry, among others.
INDUSTRIAL APPLICABILITY
[0024] The disclosed pump finds potential application in any fluid
system where it is desirous to control discharge from a pump. The
disclosed pump finds particular applicability in fuel injection
systems, especially common rail fuel injection systems. One skilled
in the art will recognize that the disclosed pump could be utilized
in relation to other fluid systems that may or may not be
associated with an internal combustion engine. For example, the
disclosed pump could be utilized in relation to fluid systems for
internal combustion engines that use a hydraulic medium, such as
engine lubricating oil. The fluid systems may be used to actuate
various sub-systems such as, for example, hydraulically actuated
fuel injectors or gas exchange valves used for engine braking. A
pump according to the present disclosure could also be substituted
for a pair of unit pumps in other fuel systems, including those
that do not include a common rail.
[0025] Referring to FIG. 1, when fuel system 10 is in operation,
first and second drivers 48, 50 rotate causing first and second
plungers 40, 44 to reciprocate within respective first and second
barrels 36, 38, out of phase with one another. When first plunger
40 moves through the intake stroke, second plunger 44 moves through
the pumping stroke.
[0026] During the intake stroke of first plunger 40, fluid is drawn
into first pumping chamber 42 via first inlet check valve 58. As
first plunger 40 begins the pumping stroke, fluid pressure causes
ball valve member 77 to engage valve seat 80 and allow displaced
fluid to flow from first pumping chamber 42 through spill control
valve 66 to low-pressure gallery 60. When it is desirous to output
high-pressure fluid from high-pressure pump 16, solenoid 31 of
actuator 30 may be energized to move spill valve member 82 toward
solenoid 31 and close spill control valve 66.
[0027] Closing spill control valve 66 may cause an immediate build
up of pressure within first pumping chamber 42. After the pressure
increases beyond a minimum threshold, solenoid 31 may be
de-energized and the force generated by the build up of pressure
against hydraulic surface 84 firmly holds spill control valve 66 in
a closed position. As the pressure continues to increase within
first pumping chamber 42, a pressure differential across first
outlet check valve 70 produces an opening force on outlet check
valve 70 that exceeds a spring closing force of outlet check valve
70. When the spring closing force of first outlet check valve 70
has been surpassed, first outlet check valve 70 opens and
high-pressure fluid from within first pumping chamber 42 flows
through first outlet check valve 70 into high-pressure gallery 68
and then into fuel rail 20 by way of fluid passageway 18.
[0028] One skilled in the art will appreciate that the timing at
which actuator 30 is energized determines what fraction of the
amount of fluid displaced by the first plunger 40 is pumped into
the high-pressure gallery 68 and what is pumped back to
low-pressure gallery 60. This operation serves as a means by which
pressure can be maintained and controlled in fuel rail 20. As noted
in the previous section, control of the energizing of actuator 30
is provided by signals received from electronic control module 28
over communication line 32.
[0029] Toward the end of the pumping stroke, as the angle of the
portion of first driver 48 causing first plunger 40 to move
decreases, the reciprocating speed of first plunger 40
proportionally decreases. As the reciprocating speed of plunger 40
decreases, the opening force caused by the pressure differential
across first outlet check valve 70 nears and then falls below the
spring force of first outlet check valve 70. First outlet check
valve 70 moves to the closed position to block fluid through first
outlet check valve 70 when the opening force caused by the pressure
differential across first outlet check valve 70 falls below the
spring force of first outlet check valve 70.
[0030] After first plunger 40 completes the pumping stroke and
begins moving in the opposite direction during the intake stroke,
the pressure of the fluid within first pumping chamber 42 creates a
force caused by the pressure differential across spill valve member
82 that nears and then falls below the force exerted by biasing
spring 88. As the pressure differential across spill valve member
82 becomes less than the spring force of biasing spring 88, biasing
spring 88 moves spill valve member 82 from solenoid 31 to the open
position.
[0031] As second plunger 44 switches modes from filling to pumping
(and first plunger 40 switches from pumping to filling), ball valve
member 77 moves to the other side of its cavity engaging valve seat
78 to block fluid flow from first pumping chamber 42 and opening
the path between pumping chamber 46 and spill control valve 66,
thereby allowing spill control valve 66 to control the discharge of
second pumping chamber 46. Second plunger 44 then completes a
pumping stroke similar to that described above with respect to
first plunger 40.
[0032] Several advantages are realized because selector valve 76 is
a ball-type selector valve. The geometry of valve body 75 that
accommodates ball valve member 77 may be simple allowing for
conventional manufacturing processes and equipment. Implementing
conventional manufacturing processes and equipment may result in a
pump that is less expensive and takes less time to produce. In
addition, because ball valve member 77 relies on line sealing
rather than surface sealing, less restrictive manufacturing
tolerances may be implemented that result in further reduced
manufacturing time and cost.
[0033] It will be apparent to those skilled in the art that various
modifications and variations can be made to the pump of the present
disclosure.
[0034] Other embodiments of the pump will be apparent to those
skilled in the art from consideration of the specification and
practice of the invention disclosed herein. It is intended that the
specification and examples be considered as exemplary only, with a
true scope of the invention being indicated by the following claims
and their equivalents.
* * * * *